The present invention relates to a bin for use in a mail transporting apparatus, which includes a plurality of vertical slots closeable by pivotably movable doors and more particularly, to such a bin having an improved door construction which serves to reduce noise and vibration.
Mail transporting apparatus, such as those currently in use by the United States Post Office, employ mail sorting bins that are supported on rollers and travel through the sorting system on tracks. Each bin includes a plurality of parallel vertical slots. Each of the slots is open at its upper end to receive mail and closeable at its lower end by a pivotably movable door. The door includes a tab extending outwardly from a first end and a lever attached to the second end. The tab is configured to cooperate with a bias spring which urges the door into an open position. The lever is engaged by a cam surface on a rocker arm which holds the door in a closed position.
As the bin passes through the mail sorting system, mail is deposited in the slots through their respective open upper ends. As the bin passes over a location at which mail is to be discharged, the rocker arm holding the lever attached to the appropriate door is moved releasing the lever and permitting the bias spring to move the door to its open position. The mail then falls through the bottom of the slot.
When the metal doors closing each of the bin slots open to drop the mail the resulting metal to metal contact causes a loud unpleasant noise. A similar noise results on the closing of the door. The impact of the door opening and closing also causes undesirable vibrations within the bin which can cause increased maintenance problems. In addition to the noise of opening and closing doors the lever is detachably fixed to the second end of each door by a pin and tab arrangement which can rattle causing considerable noise. Lastly the doors which are held in closed position by the bias spring and tab, can and do move relative to the slotted side of the bin so that they rattle extensively as the bin moves. The noise eminating from a number of such bins each having a number of doors opening and closing rapidly is a formidable problem. The resulting noise can raise to the level of health hazzard for those who must work around a mail sorting system, and the resulting impacts cause extensive maintenance problems in the bins.
A partial solution to the above problem has been implemented by the United States Post Office in which the tab extending from the first end of each door is substantially coplanar with the door. Notches are cut in a side wall of the bin to permit each such tab to extend beyond the bin side wall where it is held between two torsion springs. The first such spring bias the door so that it opens and damps vibrations and noise when the door slams shut. The second torsion spring limits the movement of the door on opening. The springs associated with each door are carried by an arm supported by the axle about which an adjacent door is pivotable. Of course, the arm for the last door of the bin must be supported by a pin provided specifically for that purpose.
An improvement on the above described mail sorting bins utilized by the Post Office is disclosed in U.S. Pat. No. 4,022,340. In this patent the tab engaged by the damping torsion springs includes a first portion which extends at a right angle to the door and a second portion which extends parallel to the door to a point beyond the bin side wall. This arrangement eliminates the need for notches in the bin sides to accommodate the tabs.
Although the above solutions serve to decrease somewhat the metal to metal impact clatter of opening and closing doors they by no means eliminate it. The rattling of closed doors against the bin frame while again decreased by the bias torsion spring is still present. Neither of these solutions treat the problem of the rattling between the lever mechanism and the door.
The detachable lever arrangement of the prior art is a weak point in the bin which can fail if either the pin or tab which extends outwardly from the door to hold the lever in place are bent in use causing the door to jam open or closed. In addition the tab extending outwardly from the door end must of necessity fit loosely within a slot in the lever to hold the lever in proper substantially coplanar orientation relative to the door. This results in substantial rattling between the lever and the door tab. Similar rattling occurs between the lever, the pin holding the lever to the door and the door itself.
The door construction of the present invention provides a unitary door and lever thereby providing a stronger door and one in which no rattling can occur between the door and the trip lever. Noise resulting from the opening and closing of the door as well as the vibration of the door against bin structure is greatly decreased by providing a door of a resilient plastic material which damps clatter. The use of a plastic material for the door has the additional advantage that it permits a unitary molded structure including both the door and the lever to be inexpensively made.